fix serial check in markdown

Author: Godmartinz

resources/views/mail/markdown/checkin-license.blade.php

@@ -10,7 +10,7 @@
 @if (isset($license->manufacturer))
 | **{{ trans('general.manufacturer') }}** | {{ $license->manufacturer->name }} |
 @endif
-@if (($target instanceof \App\Models\User && $target->can('view', $license)) ||($target instanceof \App\Models\Asset && $license_seat->user->can('view', $license)))
+@if (($target instanceof \App\Models\User && $target->can('view', $license)) ||($target instanceof \App\Models\Asset && $license_seat->user?->can('view', $license)))
 | **Key** | {{ $license->serial }} |
 @endif
 @if (isset($item->category))

resources/views/mail/markdown/checkout-license.blade.php

@@ -16,7 +16,7 @@
 @if (isset($license->category))
 | **{{ trans('general.category') }}** | {{ $license->category->name }} |
 @endif
-@if (($target instanceof \App\Models\User && $target->can('view', $license)) || ($target instanceof \App\Models\Asset && $license_seat->user->can('view', $license)))
+@if (($target instanceof \App\Models\User && $target->can('view', $license)) || ($target instanceof \App\Models\Asset && $license_seat->user?->can('view', $license)))
 | **Key** | {{ $license->serial }} |
 @endif
 @if ($note)